Device for partial deflection of a conical pencil of imaging rays



G. HANSEN Dec. 30, 1930.

DEVICE FOR PARTIAL DEFLECTION OF A CONICAL PENCIL OF IMAGING RAYS FiledApril 17, 1929 [n v'en/or:

n-an. 4"

UNITED STATES PATENT OFFICE GERHARD HANSEN, OF JENA, GERMANY, ASSIGNORTO THE FIRM: CARL ZEISS, OF JENA, GERMANY DEVICE FOR PARTIAL DEFLECTIONOF A CONIGAL PENCIL F IMAGING RAYS Application filed April 17, 1929,Serial No. 355,965, and in Germany April 23, 1928.

It is a well-known fact that, for separating part of the rays from aconical pencil of imaging rays, the application of a lano-parallel glassplate, whose rear surface may be pro- 3 vided with a translucent mirror,has the disadvantage of rays being reflected by both surfaces. If noprovision were made to destroy one of the two reflected ray pencils,which, however, causes a certain loss, double images would be theresult. The said loss can be avoided if, instead of being converging ordiverging, the rays of the imaging pencil are made to be parallel toeach other. For this reason the proposal was made that the imaging raysshould run parallel to each other within a certain part of their pathand divide in the said part. In such a way and in spite of the fact thatnow the two pencils of imaging rays that are reflected on the surfacesof the mirror can be utilized, the losses are restricted but by no meanscompletely avoided, because the additional lenses, that to produce suchan effect had to be provided in the path of the rays, give rise to newsources of losses, which, owin to the strong magnification of the image,t at frequently is made necessary here, prove to be disadvantageousespecially in the miscroscopic and Inicrophotographic path of theimaging rays.

To completely avoid the said losses is the aim of the invention. Thisaim is attained when, according to the invention, there is used as amirror a wedge-shaped plate of glass or similar transparent materialhaving dimensions that will allow the two partial pencils of raysreflecting on its surfaces to combine in one image plane and to coverthe whole desired image field. This condition is met when the effectivepart of the mirror is given such a medial thickness and its wedgeangleas well as the angle at which the rays fall on the mirror are given suchsizes that always the two partial rays reflected on the surfaces, whichbelong to any of the incident imaging rays, intersect in one point inthe image plane. Here the values of the dimensions of the mirror dependupon what material is used, that is to say upon the refrac- 50 tiveindex of this material.

The drawing illustrating the invention schematically represents asection of a constructional example of a device for partial deflectionof a conical pencil of imaging rays. This device can be applied f. i.when a microscopic image of an object should be photographed, and thiswithout the necessity of interrupting the microscopic examination of theobject during the period required for photographing.

he device consists of a glass-wedge a whose medial thickness and wedgeangle are I) and a respectively. The said glass-Wedge a is provided in apath of microscopic rays and behind the microscope objective 0 withwhich a source of light d and an illuminating condenser e areassociated. The angle the axial ray incident on the glass-wedge a formswith the corresponding normal of incidence is denominated B.

The path of the imaging rays is the following: Of an object which isindicated by an arrow f and supposed to lie behind the condenser e, themicroscope objective 0 would project a magnified image which isrepresented on the drawing by a dash-line arrow g. In consequence of theapplication of the glass-wedge a and owing to the deflection of theimaging rays, which is caused by the wedge, the said image appears lessintensive in a displaced position it, whereas part of the imaging raysare reflected on the two surfaces of the glass-wedge (1, whereby on thefront surface the medial angle of reflection is equal to the angle ofincidence [3. Now the glass-wedge a itself and its osition in the pathof the rays are to be xed in such a manner that the medial distance 70of the image plane from the glass-wedge a, the medial thickness 6 of theglass-wedge, its wedgeangle on, its refractive index n and the an le ,8at least approximately come up to t e following Equation (1) which isknown in connection with interference instruments:

given, a certain value of the medial distance corresponds to a certainvalue of the angle of incidence ,8. In consideration of a correctcombination of the imaging rays of light reflected on the two surfacesof the glass wed e a not only in the optical axis but also outsi e thesame, the angle of incidence ,8 is conveniently given such a value thatthe medial distance is has a maximal value. The distance In, however, isa maximal oneas soon as the differential quotient 51k B is infinitelysmall, viz. as soon as the differential quotient of the second factorsin 5.00s B nsin 6 on the right side of the Equation (1) is infinitelysmall. When giving this factor the desi nation f(fl) the followingrelation holds good 2 mew By means of this relation the difierentialquotient flfi) 5 can be deduced:

The relations (30) cos B 0 furnishing values that cannotbe used for nand B, the differential quotient can be infinitely small only whenrelation i (4) is arrived at:

(4) (a -sin B) (1-3 sin 6) +2 sin 8 (sin B- sin' F) -0.

When transforming the Equation (4), the Equation (5) is arrived at? thelocus of deflection a medial distance 7:, consisting of a wedge oftransparent material, whereby of the medial thickness 6 of the saidwedge, its wedge-angle on, its refractive index n and the angle B, atwhich the 70 axial ray falls on the wedge, at least approximately thetwo following equations are complied with:

12 sin 5.00s 6 a n sin B 2 sinB=3n 1 /(1-3 n) -4n GERHARD HANSEN.

